@satshow
I live in USA and use Ubuntu-Gnome 17.04. I had problems with video playback until I just kept updating and upgrading the software. After bringing the problem to the attention of Vivaldi support, Ubuntu-Gnome suddenly sent me an update notice for 115 updates to several libs. After those updates, all, with the exception of "bad" videos, started running. By "bad videos I mean broken ones that don't even work on the other browsers.
Just remember to get you updates and upgrades!